Cold-Set Gelation of Commercial Soy Protein Isolate: Effects of the Incorporation of Locust Bean Gum and Solid Lipid Microparticles on the Properties of Gels

This study aimed to evaluate the ability of commercial soy protein isolate (SPI) to form cold-set gels under different pHs (5–11), pre-heating temperatures (60 °C, 80 °C), CaCl₂ (0–15 mM) and SPI (5–15%, w/v) concentrations, and also select a formulation for the investigation of the effects of incorporating locust bean gum (LBG) (0–0.3%, w/v) and solid lipid microparticles (SLM) on gels rheological and microstructural properties. Gels were evaluated in terms of visual aspect, water-holding capacity, microstructure (using confocal laser scanning microscopy and cryo-scanning electronic microscopy) and rheological properties. SPI showed higher solubilities at pHs 7 (32.0%), 9 (51.6%) and 11 (100%). Self-supported gels were obtained under several conditions at alkaline pHs. At pH 7, only systems pre-heated to 80 °C with 15% (w/v) SPI and 10 or 15 mM CaCl₂ gave self-supported gels. At neutral pH, samples showed relative structural instability, which was minimized with LBG incorporation. Formulations G_SPI (pH 7, preheated to 80 °C, 15% (w/v) SPI, 10 mM CaCl₂) and G_MIX (pH 7, preheated to 80 °C, 15% (w/v) SPI, 0.2% (w/v) LBG, 15 mM CaCl₂) were selected for emulsion-filled gels (EFG) production. Power law parameters (K′, K″), calculated from frequency sweep results, revealed that non-filled G_MIX (K′: 472.1; K″: 77.6) was stronger than G_SPI (K′: 170.4; K″: 33.6). Besides, G_MIX showed microphase separation. SLM stabilized with Tween 80-Span 80 were active fillers in EFG, altering microstructures and increasing G’, G” and the Young’s modulus (1.8 to 2.1 kPa for G_SPI and 1.4 to 2.2 kPa for G_MIX).     

Effects of Rheological Properties and Molecular Weight Distribution on the Spinnability of Soy Protein

Experiments were carried out to elucidate the correlation between gel chromatographic profiles and rheological properties of dope with respect to the spinnability of soy protein. It was found that dope prepared with 20% protein concentrate and 1.2% sodium hydroxide showed a good transition zone from rubber-like elasticity to rubber-like flow, as frequency (log ω) in limitation was increased from ?1 to 1, and also the dope showed good spinnability when prepared in the above manner. Good spinnable dopes showed three main fractions in the gel chromatographic profiles on using a Sepharose 4B gel column. The first peak was of a high molecular weight fraction (M_w > 1,000,000) eluted at the void volume, the second peak was of low molecular weight fraction (M_w < 200,000; the peak was around 10,000) eluted at the end of the gel chromatogram, and the third part was a gentle upward slope between the two peaks (1,000,000 > M_w > 200,000). It was clear that the spinnabilities and rheological properties of dope depended on differences in composition of the three main fractions mentioned.     

The Formation and Disaggregation of Soy Protein Isolate Fibril: Effects of pH

To identify the effects of charged states on the formation and disaggregation of soy protein isolate (SPI) fibril, we studied the thermal aggregation behaviors of the constituent peptides of SPI fibril (CPSF) at various pH values (2–10) and investigated the structural changes of SPI fibril with increasing pH (2–11). Results showed that CPSF would assemble into diverse shapes at different pH values, among which the aggregates contained multiple β-sheet structures at pH less than 6, but these β-sheets were stacked to form fibrils only at pH 2. The damages from the increased pH to SPI fibril structure could be roughly divided into two stages, as follows: when pH was less than or equal to 6, the morphology of fibrils changed markedly due to electrostatic neutralization; at pH larger than 6, the fibrils suffered great losses in β-sheet, causing its structure to disintegrate rapidly. This study could provide theoretical reference to improve the pH stability of SPI fibril from the aspects of preparation and structural protection of the fibril.

     

Effects of Lipids on the Rheological Properties of Aqueous Soybean Protein Dispersions

The flow properties of soybean protein–lipid–water suspension systems and coagulated gels were related to a protein–lipid interaction. For powdered soybean lecithin-added soybean protein suspension systems and their heat-induced gels, the yield stress (σ_y) and the consistency index (K) increased with increasing amounts of added lipid, but the flow behavior index (n) and the thixotropy index (TI) decreased. On the other hand, there were only small changes in the magnitudes of the thixotropic parameters and the viscometric parameters (σ_y, K and n) after adding soybean oil at various concentrations to soybean protein dispersions. These facts suggested that the formation of a protein–phospholipid complex increased the effective particle size, and that the intermolecular entanglements and linkages among the protein molecules or among the protein-phospholipid complexes were weakened by the addition of polar lipids. The thixotropy index defined in this study is available for characterizing the stress decay that occurs within soybean protein dispersions and heat-induced gels as they are sheared.     

Effect of Soy Protein Subunit Composition on the Rheological Properties of Soymilk during Acidification

The effect of soy protein subunit composition on the acid-induced aggregation of soymilk was investigated by preparing soymilk from different soybean lines lacking specific glycinin and β-conglycinin subunits. Acid gelation was induced by glucono-δ-lactone (GDL) and analysis was done using diffusing wave spectroscopy and rheology. Aggregation occurred near pH 5.8 and the increase in radius corresponded to an increase in the elastic modulus measured by small deformation rheology. Diffusing wave spectroscopy was also employed to follow acid gelation, and data indicated that particle interactions start to occur at a higher pH than the pH of onset of gelation (corresponding to the start of the rapid increase in elastic modulus). The protein subunit composition significantly affected the development of structure during acidification. The onset of aggregation occurred at a higher pH for soymilk samples containing group IIb (the acidic subunit A₃) of glycinin, than for samples prepared from Harovinton (a commercial variety containing all subunits) or from genotypes null in glycinin. The gels made from lines containing group I (A₁, A₂) and group IIb (A₃) of glycinin resulted in stiffer acid gels compared to the lines containing only β-conglycinin. These results confirmed that the ratio of glycinin/β-conglycinin has a significant effect on gel structure, with an increase in glycinin causing an increase in gel stiffness. The type of glycinin subunits also affected the aggregation behavior of soymilk.     

Influence of Soy Protein Isolate Hydrolysates Obtained under High Hydrostatic Pressure on Pasting and Short-Term Retrogradation Behavior of Maize Starch

The influences of soy protein isolate hydrolysate (SPIH) obtained during different pressure treatments for 4 h on pasting and short-term retrogradation behaviors of maize starch (MS) were investigated. The results showed solubility of MS markedly increased, whereas swelling power decreased with increased SPIH concentration and pressure. Compared with native MS, the addition of SPIH led to decrease of peak viscosity, final viscosity, setback, and breakdown, whereas pasting temperature was increased. Meanwhile, differential scanning calorimetry (DSC) analysis also showed an increase in gelatinization temperature. In addition, low-field nuclear magnetic resonance (LF-NMR) analysis indicated that the tight association of water and starch molecules was observed with increasing pressures and additions of SPIH. Confocal laser scanning microscopy (CLSM) and atomic force microscope (AFM) images indicated that SPIH obtained at 200 MPa dispersed in the MS gel system to block the formation of hydrogen bonds and inhibit the recrystallization of MS. Fourier transform infrared (FTIR) spectroscopy analysis demonstrated that the addition of SPIH resulted in a decrease in hydrogen bonds within the starch molecules and the result supported above CLSM and AFM measurement results. The results proved that the addition of SPIH could effectively influence pasting characteristics and inhibit the short-term retrogradation of MS, which can be helpful to the application of SPIH in starch-based functional foods.

     

Outstanding Freeze-Thaw Stability of Mayonnaise Stabilized Solely by a Heated Soy Protein Isolate

There is an increasing interest in the development of cholesterol-free mayonnaise through the strategy to use food-grade polymeric emulsifiers to substitute or partially substitute egg yolk. In addition, mayonnaise-type emulsions or mayonnaise are usually susceptible to freezing. The work reported that a heated soy protein isolate (SPI) could perform as an effective sole stabilizer for mayonnaise-type high internal phase emulsions (HIPEs) with an outstanding freeze-thaw stability. Such HIPEs with a self-supporting morphology could be stabilized using the heated SPI at a protein concentration (c) as low as 0.3 wt.%. Increasing the c from 0.3 to 4.0 wt.% resulted in a progressive strengthening of gel network for the mayonnaise-type HIPEs, and the formation of finer droplets. All the as-formed HIPEs exhibited an elasticity-dominated rheological behavior, with the stiffness increasing the c. The elasticity of the gel-like HIPEs at low c values (e.g., 0.3 wt.%) was mainly associated with the formation of bridged emulsions, while that at high c values was more associated with the inter-droplet hydrophobic interactions between protein-coated droplets. All the mayonnaise-type HIPEs, formed even at a c value of 0.3 wt.%, were extremely stable against the freeze-thaw treatment. The high freeze-thaw stability seemed to be unrelated to the formation of ice crystals during the freezing. All the freeze-thawed HIPEs still exhibited a high long-term storage stability against coalescence, and their elasticity on the contrary became strengthened after the long-term storage. The findings have great implications for the development of cholesterol-free mayonnaise with a high freeze-thaw stability, suitable for food formulations.

     

Influence of Transglutaminase (TGase) Enzyme on Mechanical and Bioactive Properties of Crayfish Protein Gels

Functional and bioactive properties of crayfish meat convert their surpluses in an excellent alternative for the development of food products. Thus, protein dispersions were subjected to a thermal treatment, obtaining a protein-based gel. Rheological and antioxidant properties were studied at three different pH values (2.0, 6.5 and 8.0) when the TGase enzyme was used. The pH value exerted a strong influence on the gelation behaviour, as well as on the functional properties and the antioxidant activity of the final gels. The activity of the TGase enzyme is highly influenced by the pH of the protein dispersions. The highest antioxidant activity was obtained against ABTS and the lowest when FC reagent was used, whereas the activity against DPPH was also remarkable. TGase enzyme can be used during the thermal treatment to increase the mechanical properties, which were lost when hydrolysate systems were used.     

复合改性提高大豆分离蛋白功能性的研究

目的:利用中性蛋白酶和谷氨酰胺转胺酶(TG)对大豆分离蛋白(SPI)进行复合改性,探讨对其功能性的影响。方法:通过单因素和正交实验以及电泳分析,研究了中性蛋白酶和TG对SPI的影响趋势。结果:中性蛋白酶作用的最佳工艺条件为温度60℃、时间0.5h、pH7.0、酶用量4000U/g,SPI溶解性可达97.9%。结论:经中性蛋白酶作用后,再经过TG改性,所得的聚合物不仅有很大的相对分子质量,还可以改善SPI的溶解性,并且乳化性、发泡性均有提高。     

Soybean Mosaic Virus: Vector Specificity and Coat Protein Properties

Aphid transmission studies of two soybean mosaic virus isolates have shown that both isolates are transmitted by Myzus persicae. Only one of the isolates is transmitted by Rhopalosiphum maidis. The R. madis non-transmissible isolate could be transmitted from plants co-infected with the R. maidis transmissible isolate; aphid acquisition factor did not seem to mediate this transmission. The two isolates could be differentiated by enzyme-linked immunosorbent assay experiments, but peptide mapping experiments revealed few differences between the isolates.     

Effects of Extrusion on the Emulsifying Properties of Rumen and Soy Protein

Defatted rumen protein and soy protein concentrate were extruded in a 15.5:1 L/D single-screw extruder at the optimum conditions for their expansion (150°C and 35% moisture, and 130°C and 35% moisture, respectively). Emulsions were produced with these proteins and studied by rheology and time domain low-resolution ¹H nuclear magnetic resonance (TD-NMR). Extrusion increased storage modulus of rumen protein emulsions. The opposite was observed for soy protein. Mechanical relaxation showed the existence of three relaxing components in the emulsions whose relative contributions were changed by extrusion. Likewise, spin–spin relaxation time constants (T ₂) measured by TD-NMR also showed three major distinct populations of protons in respect to their mobility that were also altered by extrusion. Extrusion increased surface hydrophobicity of both rumen and soy protein. Solubility of rumen protein increased with extrusion whereas soy protein had its solubility decreased after processing. Extrusion promoted molecular reorganization of protein, increasing its superficial hydrophobicity, affecting its interfacial properties and improving its emulsifying behavior. The results show that extrusion can promote the use of rumen, a by-product waste from the meat industry, in human nutrition by replacing soy protein in food emulsions.     

Effect of Oil Content and Composition on the Gelling Properties of Egg-SPI Proteins Stabilized Emulsion Gels

Effects of different oils on the rheological properties, textural profile, water loss (WL), oil loss (OL) and microstructure of egg-soybean protein isolate (SPI) stabilized emulsion gels were investigated at neutral pH, wherein soybean oil, olive oil and menhaden oil were used to form emulsions. The results showed that viscosity of emulsions progressively increased with the increase of oil content. Similarly, analysis of the rheological behavior of the formulated emulsion gels revealed an increase in the mechanical strength (G’) with the increase in oil concentration, indicating that oil droplets played a significant role in the formation of the gel structure. In addition, at high levels of oil, the hardness and chewiness of emulsion gels were also high, while a slight decrease in springiness and cohesiveness were observed. A linear relationship between hardness and water/oil loss was found, whereas the Pearson correlation suggested that less drainage of water may slow down the outflow of oil. The microstructural images showed a more compact network as a result of the increase of oil content in the formulation. Scarce significant differences were found among emulsion gels formulated with different oil type, suggesting oil composition played a dispensable role on the gelling properties of emulsion gels.

     

Evaluation of Interactions Between Carboxymethylcellulose and Soy Protein Isolate and their Effects on the Preparation and Characterization of Composite Edible Films

Food Biophysics - Interactions between carboxymethylcellulose (CMC) and soy protein isolate (SPI) were assessed to determine their effects on the physicochemical and morphological properties of...     

Investigation of the Effects of Hydroalcoholic Solutions on Textural and Rheological Properties of Various Controlled Release Grades of Hypromellose

Hypromellose (hydroxypropyl methylcellulose, HPMC) matrices are widely used in the formulation of sustained release dosage forms. The integrity and performance of an HPMC matrix formulation depends on rapid hydration and gel formation upon ingestion. Due to the recent alert issued by the Food and Drug Administration regarding the potential negative influence of alcoholic beverages on extended release (ER) formulations, several researchers have evaluated the potential influence of hydroalcoholic media on drug release from ER dosage forms. It has been reported that HPMC matrix formulations do not show “dose dumping” in hydroalcoholic media. The purpose of this study was a fundamental investigation on the effect of hydroalcoholic solutions (0–40% v/v ethanol) on textural and rheological properties of different viscosity grades of neat HPMC, as the functional ingredient within a hydrophilic matrix. In general, hydroalcoholic solutions had little effect on gel formation and mechanical properties of hydrated compacts, while the rheological behavior of HPMC showed dependency on the ethanol content of such solutions.     

Effects of Partial Replacement of Gelatin in High Sugar Gels with Gellan on their Textural,Rhelogical, and Thermal Properties

Effects of partial replacement of gelatin in simulated gummy confections with either high acyl or deacylated gellan on their textural, rheological, and thermal properties were investigated. Atomic force microscopy (AFM) images of high acyl and deacylated gellan revealed that both gellan types formed finely stranded networks as a result from air-drying of dilute aqueous solutions, the strand thickness of which was approximately 0.5–1 nm. Simulated gummy confections containing 5.025–7.1 % w/w gelatin, 0–0.075 % w/w high acyl or deacylated gellan, and 73–75 % w/w corn syrup and sucrose combined were prepared and analyzed using texture profile analysis (TPA) and small amplitude oscillatory shear measurements. The principal component analysis (PCA) of textural attributes obtained from TPA identified a cluster in the first quadrant formed by samples containing 7.1 % w/w gelatin but no gellan and those containing 6.025 % w/w gelatin and 0.075 % w/w high acyl or deacylated gellan. All simulated gummy confections showed storage modulus (G′) values greater than loss modulus (G″) values at 0.1 rad/s, G″ increasing more steeply with increasing angular frequency, and G′-G″ crossovers within the examined angular frequency range (0.1–100 rad/s), typical of high solid biopolymer gels. Furthermore, increasing gellan concentration at a total concentration of the gelling agents (i.e., gelatin and gellan) of 6.1 % w/w increased the melting temperature. These results attest the feasibility of improving the heat stability of gummy confections by the partial replacement of gelatin with either high acyl or deacylated gellan with maintaining textures characteristics of gummy confections containing gelatin as the only gelling agent.     

The Influence of Enzymatic Hydrolysis on Adsorption and Interfacial Dilatational Properties of Pumpkin (<Emphasis Type=Italic>Cucurbita pepo</Emphasis>) Seed Protein Isolate

Pumpkin seed protein isolate, PSPI, was enzymatically hydrolysed by alcalase to obtain pumpkin seed protein hydrolysate, PSPH. Kinetics of PSPI and PSPH adsorption layer formation at oil–protein solution interface and interfacial dilatational properties of the layers were investigated by the drop profile analysis tensiometer (PAT) in order to determine the influence of enzimatic hydrolysis on the interfacial properties of pumpkin seed proteins. The properties were investigated at different protein solution concentrations (0.0008–0.8 g/100 mL), ionic strengths (0–0.5 mol/L NaCl), and at two acidic pH (3 and 5, where PSPI’s pI?=?5). It was found that both, PSPI and PSPH, contribute to an increase in the interfacial pressure, π, at the oil–protein solution interface and form the interfacial proteinaceous films. Dilatational elasticity, E’, of the interfacial films was found to be a few times higher than the dilatational viscosity, E”, regardless of the experimental conditions. The obtained diffusion rate and adsorption rate constants, k_diff and k_ads respectively, were higher for PSPH than for PSPI. k_diff was found to increase as protein concentration was increased, and to decrease as ionic strength was increased, for both PSPI and PSPH. At pI?=?5, PSPH showed an increased π and E’, as well as mitigated influence of ionic strength on k_ads when compared to PSPI.     

Effect of the Supplementation of Sulfur Amino Acids to a Diet Containing Soy Protein Isolate on Lipid Metabolism in Rats

The effect of the supplementation of sulfur amino acids to a low casein or soy protein isolate diet on tissue lipid metabolism was investigated. Supplementation of methionine to a 8% casein diet produced a fatty liver in rats, however, supplementation of methionine to a 8.8% soy protein diet (corresponding to a 8% casein diet as to sulfur amino acids content) did not produce a fatty liver. At the level of 8% or less of soy protein in the diet, the accumulation of liver lipids and serum triglyceride was observed. An amino acid mixture simulating the composition of soy protein isolate caused significant accumulation of liver lipids, but serum triglyceride was not changed. Serum cholesterol in rats fed the soy protein diet was lower than that in rats fed the casein diet, but on feeding the amino acid mixtures simulating these protein diets, there was no difference between the two groups. The small differences between soy protein isolate and casein as to lipid metabolism might be due to the small differences in the contents of sulfur amino acids or the specific nature of the soy protein or casein. The supplemental effect of methionine and cystine was also studied. About 60% of total sulfur amino acids could be substituted by cystine for maximum growth.     

General Properties of a Plastein Synthesized from a Soybean Protein Hydrolysate

By use of pepsin a plastein was synthesized from a peptic hydrolysate of soybean protein and characterized as a protein-like substance, based on its behavior against trichloroacetic acid and its affinity to dyes. The contribution of the S–S bridge to plastein formation was little if any. The fractionation of the protein-like substance by solubility showed that the whole plastein-reaction product was constituted of 81.5 parts of the 50% ethanol-insoluble fraction; 63.8% of this fraction was also insoluble in 0.035 M phosphate buffer (pH 7.6). The phosphate buffer-insoluble fraction was mostly solubilized in 0.3 M sodium dodecyl sulfate (SDS). Although it was a minor component, there was a 50% ethanol-soluble and water-insoluble (prolamine-like) fraction which showed a reversible aggregation-dispersion change by a repeated heating-cooling treatment. A characteristic point of the SDS-soluble and prolamine-like fractions was found in their amino acid compositions. As compared with the substrate (peptic hydrolysate of soybean protein), they contained larger amounts of hydrophobic amino acids such as leucine than hydrophilic ones typified by glutamic acid.